RODI/TDS question

biecacka

biecacka

Active member
So here is my question....I have been battling nitrates for some time in my tank. 240 gallon with a med/heavy bioload in it. I use RODI water and my handheld TDS meter was reading zero so I continued to do changes as normal. In an attempt to battle nitrates I was doing 50 gallons about every 10 days and a few 100 gallon changes. Now my skimmer was offline for awhile too so I contributed some of the issues to that. Well at a lost, I was talking with my LFS and he suggested an inline TDS reader, stating they are more accurate and always right there since its in the unit. So I bought it and came home and installed it. Tested the water and guess what I saw.....175 out of the faucet reducing to 13 before RO unit and an exit of 2. So my question is if my water is at a 2 coming out of my RODI unit what impact could that have on my nitrates. They currently are 75-100. I am replacing the filters today as that is a given to me. I am just wondering if anyone knows how heavy of an impact that could have on the situation. I've done a LOT of water changes and top off with water that has had that reading. A guy at another LFS here says hat the reading out of the TDS meter has an impact of 3.5 on a scale of 1-5 on not being able to reduce my nitrates. Thoughts?

Corey
 
No, because I haven't done a batch of saltwater since I realized that the RODI unit was not putting out zero readings. I should just mix up a gallon or 5 and take a reading to see.

Corey
 
This isn't rocket surgery - do a nitrate test on your RO out. You can calibrate the good tds meters, which might be worth a shot.

However, even if both those ppms are pure nitrate, 2 ppm nitrate in the RO isn't going to turn into 75-100 nitrates in your tank, so regardless of the RO/DI problem or lack thereof, you have a nitrate factory in your tank.
 
I not accusing it of causing nitrates of 75-100. That is attributed to 21 fish with heavy feedings and a poorly functioning skimmer over the course of about 18 months or so. I'm only trying to figure out the impact it might have. Doing water changes with nitrate infested waters arent helping. I tested the water, did a 100 gallon water change and the nitrates in the tank stayed close to the same via the test. So there is some impact. I know ppl who change filters at 1ppm and others who,let it ride up to 5. Just wondering what the impact of basically having a tank full of water that didn't come out at 0 is over the long haul.

Corey
 
MondoBongo said:
in my opinion it depends on what those 2ppm are made of.

it's entirely possible that you're getting nitrates in from those dissolved solid, the EPA's limit on nitrates in drinking water is a whopping 10PPM:

https://safewater.zendesk.com/hc/en...EPA-s-drinking-water-regulations-for-nitrate-

here is the expanded list:

http://www.epa.gov/your-drinking-water/table-regulated-drinking-water-contaminants

have you ever tested any newly made saltwater for nitrates?
Click to expand...


I agree it all depends on what is in that TDS reading. Could be harmless or could be deadly like copper. There's copper in the water going into my house and I have copper pipes. I switched out my DI resins as soon as 1ppm was shown. I now have multiple DI states and swap out slightly sooner now.

Some people however have perfectly fine water and after adding something like prime have used their tap water for years with no issues. RO/DI is a safe and prudent investment. As you never know when the water quality will change temporarily or permanently.
 
As others noted, I rather seriously doubt the 2 ppm or so in your output water has much to do with the nitrate problem in your reef. The only exception would be if those 2 ppm were composed of a good deal of copper, chlorine or ammonia. The first two would potentially poison some of the life on your live rock, which would add to the bioload of the tank. The third possibility would simply be adding to the nutrient load, albeit at a much smaller % than the fish and fish food are adding nutrients to the equation.

If I were in your shoes, I'd very strongly consider carbon dosing. Water changes just don't help all that much when battling nitrates or phosphates, except perhaps to make a large dent in the tank water concentration immediately before starting vinegar/ethanol additions.
 
That's my thoughts too. I started vinegar/vodka dosing 10 days ago so it's underway. Was waiting for my new skimmer as I know it's an important part to carbon dosing. I was confused/worried slightly when a guy told me that 2 out if my RODI unit is likely the largest reason my water is out of whack. Not the fact I have 20 fish and feed heavily. :lol:

Corey
 
I agree that copper and similar toxic compounds would be a lot more dangerous than a bit of nitrate. Nitrate at 75-100 ppm should be safe for fish and soft corals. Most likely, the nitrate is coming from food or detritus. I'd run a nitrite test, if that were easy, since nitrite will confuse nitrate test kits. A second opinion on the nitrate test kit might be useful, too.

Some of the more common sources of this type of problem are feeding problems, coarse substrates, artificial filtration like bio-balls, and a lack of sufficient live rock.
 
Jon, I have about 250-300 pounds of live rock, 80lbs of sand. It's a finer sand too, I do feed semi heavy since I have so many fish. I have cut down on the feeding tho, I had no skimmer producing skim for 18 months. I have double checked the nitrates but will check the nitrites as well. I don't have bio balls in, but I did recently add a marinepure block, the larger one. Last week it was added as well as vinegar/vodka dosing. I know this is a lengthy process to defeat them, I just want to make sure I am on the right path.

Corey
 
There are some of us that are quite reluctant to use MarinePure bio-blocks or any other brand of sintered artificial ceramic substrates for biological filtration because of their aluminum content.

Just thought I would note this if you hadn't heard of this before.
 
I'm on that hesitant side. I haven't seen anything to say it's safe nor anything to say it definitely is detrimental in the short or long run.

This is a decent thread of going back and forth on it's Al content. Nothing conclusive.
http://www.reefcentral.com/forums/showthread.php?t=2453931

But it's not magic as you know it's just a method of proving surface area. Rock does that too and to me is safer. I don't like the reports of the marine blocks, sheets, balls, etc. falling apart. Sure it provides 1000 football fields of surface area(not accurate) but is that really necessary?
 
I have been following the thread mentioned above. Unfortunately in my apartment I am limited with sump space so I have a 75 as a sump. 30lbs of Rock in it and the skimmer. Few other things like heaters, temp probe etc. I have a decent amount of live rock in tank but would love more for filtration but it's not feasible to have more in a serviceable way. Sure I could put them in a few brutes under the stand and tie them to the system and keep water flowing brought them. But if debris got here I could have no removal method. Or no easy one at least.
I considered the siporax as well as it seems to have very solid reviews. Who knows, maybe once I get this under control I can remove the block. Not sure yet, but I'll be keeping an eye on it.

Corey
 
You already have a reasonable amount of live rock and a sand bed, I think it's unlikely that a marine pure or other brand of sintered ceramic will change much, because you already have a good deal of anoxic surface area within the pores of the live rock.

The carbon dosing is key, as it tends to bootstrap the bacteria that denitrify nitrate into nitrogen gas, as well as promote the growth of heterotrophic bacteria in the water column that are then removed by the skimmer (which removes nitrate, phosphate and carbon).

Depending on the tank, some of us have found that after the initial dosing regime, enough denitrification bacteria are established in the tank to discontinue carbon dosing and still maintain near zero nitrate levels.
 
My water pre-ro is 663 on the tds. I've been running 35 on the out for almost a year, but recently changed the cartridges when it spiked to 175. I used to have an issue with nitrates until I added some calerpa to my fuge. I've been at 0 for 6 months now. I'm no expert, nor am I positive this is a solution, just my $.02
 
Depending on how much food is entering the system, the tank might benefit from more live rock, although the amount in the tank is reasonable, if perhaps towards the light side. You could look into a denitrator if the level bothers you. A refugium with macro algae might help a lot, too, although it'd be more expensive to run because of the lighting needs.
 
I only use RO for my water change and the RO out put is about 4-8 ppm. I would not worry about using DI, too expensive for the minimal improvement, if any to the water. I do have a water solftener for the whole house. I have been keeping reef tank for 20 years, marine for 30+ years and have never got on the RO band wagon
Your RO/DI water out is not your problem.
I have always use a sand bed. I do have moderate amount of bio load and never have nitrate detectable in my system.

I recommend that you add a refugium with macro algae and sand bed. You can see the denitrification process clearly in the sand and see nitrogen bubble at about .75 inches deep in the sand.
 
OrionN said:
I only use RO for my water change and the RO out put is about 4-8 ppm. I would not worry about using DI, too expensive for the minimal improvement, if any to the water. I do have a water solftener for the whole house. I have been keeping reef tank for 20 years, marine for 30+ years and have never got on the RO band wagon
Your RO/DI water out is not your problem.
I have always use a sand bed. I do have moderate amount of bio load and never have nitrate detectable in my system.
....
Click to expand...
That can be very misleading.

For some that maybe OK. For others a disaster.

There are some that can safely use straight tap water for decades with no issues. TDS readings is not an indication of water quality. A TDS of 1000 could be just fine. A TDS of 1 could be leathal. It all depends on what is generating that reading. A 1TDS reading for me means copper = invert death.

Also, we never know when the water quality degrades enough to be an issue for our tanks yet perfectly fine for human consumption so no alerts go out to the public.
 
Last edited:
RO system are designed to remove certain dissolved solid from our tank. Not all dissolved solid are removed with the same efficiency. I my my case we have a total house water softener which essentially exchange all dissolved solid to NaCl

RO membrane filter by ionic charges. Ions are essentially all removed. Non ionic solid just does not dissolve well in water, so it is not something that we worry about it too much.
The carbon remove most large molecules from the water.
In our drinking water, the one thing that give us (human) no problem but deadly to our tank if built up is copper. Copper as an ions are essentially all removed by the RO membrane.

Well maintain RO system, meaning carbon not exhausted, now or ever before, and RO membrane in good condition (high hardness mainly CaCO3 can really clot up the membrane, and spend Carbon cartridge can allow Chlorine to destroy the membrane, dry out membrane can break and thus cannot filter well anymore) should remove essentially everything need to be remove from the water so that we can use it for our tank.
 
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